A senator is overall an ordinary player who has served the community well and has been bestowed the rank of a Senator as a tribute by CipSoft GmbH. Senators retain an advisory function but they do not have any active power of e.g. Gamemasters. The decision as to whether or not a former helper is invited to become a Senator rests with CipSoft.
When the voluntary Gamemaster position was removed, Gamemasters had the choice whether to become Senators or Senior Tutors.
More detailed information can be read in the official FAQ